High aspect ratio, polymer nanotubes (PNTs) and nanowires exhibit remarkable electrical, thermal, and mechanical properties which can be attributed to preferential chain alignment and high surface area to volume ratios. For example, polythiophene nanotube array thermal interface materials (TIMs) (Singh, V., et al. Nat. Nanotechnol. 2014, 9, 384-390) and polyethylene nanowire arrays (Cao, B. Y., et al. Polymer 2011, 52, 1711-1715 and Cao, B. Y., et al. Heat Transfer Eng. 2013, 34, 131-139) have been reported that exhibit dramatically improved anisotropic thermal conductivity. There have also been multiple reports on the use of vertically aligned, high-aspect-ratio polymer nanotubes to create surfaces with superhydrophobic and tunable wetting properties (Cao, B. Y., et al. Heat Transfer Eng. 2013, 34, 131-139; Jin, M., et al. Adv. Mater. 2005, 17, 1977-1981; Mao, C., et al. J. Mater. Chem. 2009, 19, 9025-9029; Liao, Y. C., et al. Nanosci. Nanotechnol. 2013, 13, 2729-2734; and Xu, J., et al. Colloids Surf, A 2007, 302, 136-140).
Typically, for wetting and thermal interface applications, nanotube arrays are grown on a substrate where the bottom of the array is anchored and the other end consists of free tips. Due to the wet processing conditions used, and because the densely packed tubes have high aspect ratios, the vertical arrays have the tendency to bundle and aggregate during processing through elastocapillary coalescence (Cao, B. Y., et al. Heat Transfer Eng. 2013, 34, 131-139; Jin, M., et al. Adv. Mater. 2005, 17, 1977-1981; Xu, J., et al. Colloids Surf, A 2007, 302, 136-140; and Duan, H. et al. Nano Lett. 2010, 10, 3710-3716), which occurs when capillary forces cause objects to elastically bend into contact with each other upon which the objects stick together through adhesion. Nanotube aggregation can dramatically alter the surface morphology and the corresponding interactions between the PNT array and a contacting liquid or substrate.
Despite their high intrinsic thermal conductivities, thermal contact resistance (TCR) has been a major limitation of high aspect ratio structures such as carbon nanotube (CNT) array TIMs (Cola, B., et al. J. Appl. Phys. 2007, 101, 054313; Taphouse, J. H., et al. Adv. Funct Mater. 2014, 24, 465-471; and Tao, T., et al. IEEE Trans. Compon., Packag., Manuf. Technol. 2007, 30, 92-100). Furthermore, the favorable mechanical properties and strong adhesion of soft materials suggests that PNTs could potentially reduce the high contact resistance associated with traditional nanotube interfaces.
Bulk polymers, however, are commonly considered thermal insulators owing to their low thermal conductivities, which are typically on the order of 0.2 Wm−1K−1 at room temperature. The low thermal conductivity of these materials is caused by the random orientation of the molecular chains in amorphous regions (Choy, C. L., Polymer 1977, 18(10), 984-1004; and Henry, A. Ann Rev Hear Transfer 2013:DOI: 10.1615/Annual Rev Heat Transfer. 20 13006949.1, 2, which reduces the mean free path of heat conducting phonons. Previous studies to enhance the thermal conductivity of polymers have thus focused on semi-crystalline polymers which can degrade at temperatures as low as 125° C.
Furthermore, previously reported methods drawn to the fabrication of high aspect ratio polymer nanostructures with tunable surface morphology, and thus surface properties, remain relatively complex, often relying on lithographic processes, special drying conditions, or varying structure dimensions, so there is a need to develop simple and facile approaches (Liao, Y. C., et al. Nanosci. Nanotechnol. 2013, 13, 2729-2734; Xu, J., et al. Colloids Surf, A 2007, 302, 136-140; Duan, H. et al. Nano Lett. 2010, 10, 3710-3716; Dawood, M. K., et al. Soft Matter 2012, 8, 3549-3557; and Kang, S., et al. ACS Nano 2010, 4, 6323-6331). In another example, nanoscale hierarchy has shown to create surfaces with tunable wetting properties (U.S. Publication No. 2013/0062204 and U.S. Pat. No. 8,293,140), but the methods described involved the use of complex, multi-step deposition processes.
Thus, facile methods for forming nanostructured polymer-based arrays with tunable properties remain a challenge.
Therefore, it is an object of the invention to provide polymer-based nanostructured materials with surface morphologies which can be selectively tuned in order to control the surface wettability, thermal, and electrical properties of the materials.
It is a further object of the invention polymer-based nanostructured materials demonstrating chain alignment within a purely amorphous polymer material with tunable properties.
It is a further object of the invention to provide methods of making such polymer-based nanostructured materials with tunable properties, and uses thereof.